1. Field of the Invention
The present invention relates to an ink jet printing method and an ink jet printing apparatus which print an image on a print medium while performing a cleaning operation for removing a substance (thickened ink or dirt) hindering ejection of ink, at a preset timing.
2. Description of the Related Art
Printing apparatuses (ink jet printing apparatuses) are widely used which print images by ejecting ink to print media such as print sheets. To eject ink, the ink jet printing apparatus uses a print head having a plurality of nozzles and ink ejection ports (outlets of the nozzles) formed therein. The plurality of ink ejection ports (hereinafter referred to as “ejection ports”) are formed on an almost flat ejection port forming surface (hereinafter referred to as an “ejection port surface”) of the print head. Two types of print heads are available; one of these types of print head ejects ink while moving in a main scanning direction together with a carriage, and the other type of print head (line head type) ejects ink while fixed and stopped. The former type of print head is used for ink jet printing apparatus based on what is called a serial scan scheme. The other type of print head is used for what is called full line type ink jet printing apparatuses.
With these printing apparatus, if thickened ink or dirt (the substance hindering ink ejection) is collected around the nozzles or ejection ports in the print head during an image printing operation or standby (non-printing operation), the ink may be inappropriately ejected or printed images may be degraded. As a technique for solving this problem, a cleaning technique is known such as pressurization recovery, wiping, or preliminary ejection (idle ejection). The pressurization recovery is a process of pressurizing the interior of the print head to push the thickened ink, bubbles, dirt, or the like out of the nozzles. The wiping is a process of wiping the ejection port surface using a cleaning blade (cleaning member) made up of an elastic body. The preliminary ejection (idle ejection) is a process of ejecting ink from the print head in order to remove the thickened ink or dirt instead of printing images.
For the cleaning operation, the image printing operation must be temporarily suspended. Japanese Patent Laid-Open No. 2005-349841 describes a technique of performing a cleaning operation during the non-printing operation to reduce delay resulting from the cleaning operation. Furthermore, Japanese Patent Laid-Open No. 2004-358791 describes a technique of periodically performing the cleaning operation on the basis of instructions from a host computer to reduce the time for which the printing operation is suspended owing to the cleaning operation.
However, with a large printing volume (the amount of printing during a consecutive printing operation of consecutively printing images), even though the cleaning operation is performed before the consecutive printing operation, the cleaning operation may need to be performed again during the consecutive printing operation. In this case, the above-described conventional techniques cannot reduce the suspension time for the printing operation. That is, the cleaning operation is performed during the consecutive printing operation. The cleaning operation is started at the timing (cleaning timing) when a predetermined condition is met. The condition is often set on the basis of the total amount of ink ejected from the print head, a change in the condition of the print head, or the like. Therefore, the printing apparatus automatically starts the cleaning operation when the condition is met. Thus, the printing operation is suspended at a user's unintended timing, and the cleaning operation is started.
An ink jet printing apparatus (commonly called a label printer) is known which consecutively prints images on a plurality of labels temporarily attached to a band-like card board so as to be arranged in a longitudinal direction. The label printer may be used to print images on the labels in synchronism with an external instrument. A label attaching operation may be performed during a post-process after the printing operation of the label printer has been completed. Thus, if the printing operation is suspended at the user's unintended timing as described above, the label printer may fail to synchronize with the external instrument or the post-process operation may be complicated.
Furthermore, one type of label printer has a function of allowing the user to pre-instruct the printer on a unit for batch printing (the unit for consecutive printing of images on a plurality of labels) (see, for example, Japanese Patent Laid-Open No. 62-182029 (1987)). This type of label printer is effective in printing images of the same content on a plurality of labels. If the labels have different print contents, when the printing operation is suspended at the user's unintended timing as described above and instead the cleaning operation is performed, the above-described problems, that is, the failure to synchronize with the external instrument and the complicated post-process operation, become more serious.
Furthermore, a full line type ink jet printing apparatus having a plurality of the line head type print heads arranged in a print medium conveying direction has a long distance between a print head located on the most upstream side of the print medium conveying direction and a print head located on the most downstream side of the print medium conveying direction. Thus, for example, a print medium positioned below the print head on the conveying direction most upstream side may be different from a print medium positioned below the print head on the conveying direction most downstream side (the succeeding print medium and the preceding print medium). To suspend the printing operation for the cleaning operation, it is necessary to complete printing the print medium on which the image is being printed (preceding print medium), then discharge the preceding print medium, and move the succeeding print medium to a downstream position in the conveying direction where the succeeding print medium does not hinder the cleaning operation, before performing the cleaning operation. Consequently, when the printing operation is restarted after the cleaning operation has been completed, the print medium on which the corresponding image has not been completely printed yet is moved to the position where image printing is possible. This requires a process of conveying the succeeding print medium in a direction opposite to the conveying direction (back feed). This may in turn further degrade productivity, prevent the printing apparatus from synchronizing with the external instrument, or complicate the post-process operation.